If the R-rate spikes in London, overnight stays could be banned and people told not to travel in and out of the capital, the Sunday Times reported.
[“The M25] would be the border point,” an insider told the paper.
Other potential measures include “personalised risk scores” for people aged between 50 and 70, adding to the 2.2 million people who were previously asked to take part in the shielding program.
Downing Street sources distanced themselves from the detail in the reports, calling them “speculative”, PA Media reported.
The shielding advice was only lifted on Saturday for those in England, Scotland and Northern Ireland, and remains in place until August 16 for those shielding in Wales.
But 24 hours earlier Mr Johnson was forced to announce a slow down of the lockdown easing, with planned relaxations for the leisure and beauty sectors delayed after a rise in Covid-19 cases was recorded.
The prevalence of the virus in the community is thought to be rising for the first time since May.
On Wednesday Mr Johnson reportedly held a “war game” session with Chancellor Rishi Sunak to run through possible options for averting another nationwide lockdown.
On top of the alleged lockdown avoidance preparations, experts have speculated that ministers might have to order the closure of pubs, which were permitted to start serving again on July 4, if schools are to reopen fully in September.
Professor Graham Medley, a member of the Scientific Advisory Group for Emergencies (Sage), said earlier a “trade off” could be required if the Prime Minister’s pledge is to be met.
His comments followed chief medical officer Professor Chris Whitty’s remarks that the country was “near the limit” for opening up society following the coronavirus lockdown.
A No 10 source told the Sunday Times: “Another national lockdown is like our nuclear deterrent — we will never rule it out but it should be the very last resort in the fight against Covid.”